1. Field of the Invention
This invention relates to a method of recording an information signal on a disk-shaped recording medium. This invention also relates to an apparatus for recording an information signal on a disk-shaped recording medium. Furthermore, this invention relates to a disk-shaped recording medium such as an optical disk or a magneto-optical disk.
2. Description of the Prior Art
Japanese published examined patent application 3-52148 discloses a system for recording an information signal on a disk-shaped recording medium. In the system of Japanese application 3-52148, the recording medium has a coat of photosensitive material, and a laser light beam modulated in accordance with the information signal is focused into a spot on the recording medium. The light-reflective characteristics of the light-spot receiving fraction of the recording medium change in response to the present time segment of the information signal. This means the recording of the present time segment of the information signal on the fraction of the recording medium.
In the system of Japanese application 3-52148, during the recording of the information signal, the recording medium is rotated about its center while being exposed to the light spot. At the same time, the center of the recording medium is linearly moved relative to the position of the light spot along a direction such that the light spot will move radially with respect to the recording medium. As a result, the recording medium is scanned by the light spot along a spiral line. The spiral line corresponds to a spiral track along which the information signal is recorded. The spiral recording track may be replaced by an array of concentric circles of recording tracks.
In the system of Japanese application 3-52148, during the recording of the information signal on an inner region of the recording medium, the rotation of the recording medium is controlled so that the light spot will continue to move relative to the recording medium at a constant linear velocity. On the other hand, during the recording of the information signal on an outer region of the recording medium, the recording medium remains rotated at a constant angular velocity. The boundary between the inner region and the outer region of the recording medium is chosen to correspond to a given radius of curvature of the recording track.
Japanese published unexamined patent application 5-303746 discloses a disk-shaped recording medium which has a spiral recording track. In one example of the recording medium disclosed by Japanese application 5-303746, the pitch between neighboring track segments decreases as a fractional region including the track segments radially moves toward an outer edge of the recording medium. In another example of the recording medium disclosed by Japanese application 5-303746, the pitch between neighboring track segments decreases and then increases as a fractional region including the track segments radially moves toward an outer edge of the recording medium.
Generally, the performances of the recording and reproduction of an information signal on and from an outer portion of a disk-shaped recording medium tend to be lowered by various factors such as a swing of a disk plane or an eccentricity of a center hole of the recording medium.